Co-Mn Based Oxides Morphology Modulation And Energy Storage Characteristics Research

Under the top-level design of the carbon peaking and carbon neutrality goal in2023,energy is the top priority in achieving the dual carbon goal.In order to push the world forward to pass through the critical point of green energy,achieving the qualitative goal of"strengthening dual energy control and improving energy efficiency"economic systems is one of the greatest scientific and social challenges of our time.As a representative new type of energy storage device,supercapacitors（SCs）can fill the gap between secondary batteries and traditional capacitors with their unique advantages of high power density and long cycle lifespan,which is of great significance for the development and application of rapid and sustainable energy storage systems.Optimizing highly active materials by regulating their morphological structure and surface/interface properties to achieve fast and efficient charge and mass transport is the key to solving the slow charge storage kinetics.On the one hand,micro-nano modulation of the morphological structure improves the structural stability and the number of reactive sites.on the other hand,surface/interfacial defects of the material play an important role in the enhancement of reactive site activity.Therefore,this thesis focuses on the two perspectives of morphology and structure modulation,as well as the design of oxygen-deficient heterostructures to enhance the structural stability of the materials,optimize the reactive site activity,and improve the ion storage capacity.In addition,the mechanism of defects and heterostructures on the energy storage behavior is analyzed by DFT simulation.The specific research content and conclusions are as follows:（1）By designing different dealloying process parameters,multi-stage pore structures of NiO/CoO（O_V）containing oxygen defects were synthesized using ternary Al-based alloys as precursors.The results show that NiO/CoO（O_V）exhibits excellent adsorbed EDLC capacitance and redox pseudocapacitance co-dominated energy storage due to the high theoretical specific capacitance of CoO and the highly active oxygen-deficient NiO（O_V）.It has an ultra-high area-specific capacitance of 18.4F/cm²at a current density of 10 m A/cm².The results of DFT results show that the oxygen vacancies effectively regulate the charge distribution at the interface and enhance the adsorption capacity.As preferred reaction active site,oxygen vacancies play a more significant role in enhancing the NiO activity for NiO/CoO（O_V）multilevel pore structure materials.（2）In view of the promotion of oxygen defects for adsorption capacity in the previous section,（Co,Mn）（Co,Mn）₂O₄/CoO/Al₈Mn₅（O_V）three-phase nanoneedle arrays have been prepared in this chapter by introducing oxygen defects c-a heterostructure via a simultaneous heterophase dealloying strategy.It exhibits redox pseudocapacitance-dominated energy storage mode with a high specific capacitance of 1033.51 F/g（1A/g）and a well structural stability（5000 turns,83.70%）.DFT results show that oxygen vacancies promote the charge exchange between OH^-ions and more metal atoms,improving the charge distribution and adsorption of（Co,Mn）（Co,Mn）₂O₄.In addition,the Mn element shortens the band gap and improves the electrical conductivity of the material.When adsorbing OH^-ions,the Mn element acts as a preferential active site.In addition,the dense c-a interface with synergistic effect can not only alleviate the stress and volume changes of the material during the charge and discharge process but also increase the cycle life of the material.（3）In view of the oxygen-deficient cobalt-manganese based c-a heterostructures studied in the previous chapter,CoAl₂O₄/CoO nanosheet arrays were prepared by the dealloying method,then combined with the electrochemical deposition method to introduce the spinel-structured cobalt-manganese based crystalline-crystalline phase（c-c）oxygen-deficient CoMn₂O₄/Mn₃O₄（Ov）heterostructures,and synthesize CoMn₂O₄/Mn₃O₄/MnAl₂O₄（Ov）spinel nanosheet heterostructured composites.The results show that due to the multiple effects of CoMn₂O₄/Mn₃O₄（Ov）heterostructure and morphological structure,CoMn₂O₄/Mn₃O₄/MnAl₂O₄（Ov）exhibits an energy storage mode dominated by adsorption double-layer capacitance and redox pseudocapacitance.Its area specific capacitance is as high as 17700.32 m F/cm²（2 m A/cm²）,and the capacitance retention rate is 88.93%（5000 cycles）.The DFT results show that the oxygen vacancies could regulate the electronic coordination environment of Co and Mn atoms promote the charge transfer rate and charge transfer amount,and thus enhance the energy storage capacity of the material.In addition,due to the chemical bonding characteristics between CoMn₂O₄/Mn₃O₄（Ov）heterostructures,Co atoms are the most active reactive sites when adsorbing OH^-.In conclusion,it is shown that the design of oxygen-deficient c-c heterostructures is of great significance for the improvement of electrode activity and charge storage capacity.（4）In view of the conclusions studied in the previous chapters that the oxygen-deficient c-c heterostructures improve the electrical conductivity as well as the structural stability,transition metal oxide/rGO heterostructures（TMO（O_V）/rGO）were designed in this chapter in order to broaden the voltage window of the electrodes and improve the conductivity of the materials.Bi₂O₃/Mn₃O₄/Mn₂AlO₄（O_V）micro-nanoflowers were synthesized by dealloying combined with hydrothermal composite rGO strategy to design Bi₂O₃（O_V）/rGO and Mn₃O₄/rGO heterostructures on Bi₂O₃/Mn₃O₄/Mn₂AlO₄（O_V）micro-nanoflowers composites.The composites exhibit co-dominant energy storage mode with adsorbed bilayercapacitanceandredoxpseudocapacitance.With Bi₂O₃/Mn₃O₄/Mn₂AlO₄（O_V）/rGO as the positive electrode and rGO as the negative electrode in TEATFB/PC organic electrolyte,the power density reached 6318.38W/kg when the energy density was 333.47 Wh/kg,and the energy density was up to204.12 Wh/kg,when the power density is 31044.62 W/kg.DFT simulation results show that oxygen vacancy defects can substantially increase the activity of Mn₃O₄.TMO（O_V）/rGO formed by composite rGO mainly acted on Bi₂O₃（O_V）.The Bi₂O₃（O_V）/rGO heterojunction can provide a conductive network and more ion adsorption sites for carriers and widen the voltage window（0.8 V）,thereby achieving a substantial increase in energy density.This thesis has 121 figures,8 tables and 298 references.